Method and apparatus for noninvasive determination of a disease state of a human eye

ABSTRACT

To determine a cataract or the degree of cataractogenesis in an eye of a patient, the patient views two lights juxtaposed, wherein each light comprises a mixture of two different wavelength lights. One of the lights is a fixed reference mixture, while the mixture of the other non-fixed light is varied until the patient observes a match between the two light mixtures in terms of hue, brightness and saturation. The luminance levels of the light components of the non-fixed mixture for providing the match and the proportionate levels of the two components are then determined. The shorter wavelength light of the non-fixed mixture is then substituted with a new wavelength light and the new mixture varied again until the patient observes a match as before. Alternatively, a polarization state of the shorter wavelength light is altered before determining a new mixture for obtaining a match. The luminance levels of the light components of the new mixture are then determined and another proportion obtained representative of the proportionate levels thereof. The first and second proportions are then compared to respective proportions of a standardized group. Deviations between the proportions of the patient and the standardized group indicate the existence of a cataract and/or the degree of a cataract precursor formation.

TECHNICAL FIELD

The present invention generally relates to noninvasive determination ofdisease states. More particularly, the present invention relates to amethod and apparatus for noninvasively determining an ocular diseasestate, and for noninvasively determining the rate of development of thisocular disease state.

BACKGROUND ART

A person with a mature cataract, which significantly impairs visualfunction, can generally be treated by surgically extracting the impairedlens of the person and replacing it with either an intraocular lens oran extraocular lens. However, the condition cannot be addressed untilproperly diagnosed or determined.

Many different methods and apparatus have been developed in the past tohelp determine the existence or extent of a cataract. These methods andapparatus have generally made the determination based either on visualacuity tests or on an analysis of light exiting the eye of the patient.However, these may not be optimum indicators of a cataract, due tovarious anomalies. In the case of visual acuity tests, that depend uponlight reaching the retina, the use of high contrast letters or figuresmay enable the patient to recognize the letters and figures and thus"pass" the visual acuity test regardless of a cataract condition.

Similarly, in another test which compares a photograph of a person'slens to a standardized series of photographs of a lens with differentdegrees of cataract formation in different parts of the lens, theresulting photographic images depend upon back scattered light from thelens. Because the back scattered light may not correlate highly with thelocation of the cataract and what the patient sees, a clinician usingthe photographs as the basis of an analysis will not be able toaccurately determine the effect of opacities upon the patient's visualfunction and accordingly the patient may "pass" or may "fail" the testincorrectly. Moreover, in U.S. Pat. No. 4,863,261, issued to J. Flammer,entitled "Method of and Apparatus for Measuring the Extent of Cloudingof the Lens of a Human Eye," light exiting the eye, i.e. "backscattered" light, is analyzed with respect to incident radiation todetermine the extent of clouding of the lens.

Benedek et al., in U.S. Pat. No. 4,993,827 for "Method for DetectingCataractogenesis", issued Feb. 19, 1991, collect and determine theintensity of light scattered from a measurement location in the lens andcompares this value to the intensity of light scattered by a normal,clear lens to determine the degree of cataractogenesis at the specificmeasurement location.

Taratuta et al., in U.S. Pat. No. 5,072,731 for "Apparatus for DetectingCataractogenesis Using Quasielastic Light Scattering", issued Dec. 17,1991, analyze the light scattered from the lens using an autocorelationfunction or the power spectrum to separate the light fluctuation intotwo components: one caused by fast diffusing proteins and one caused byslow diffusing protein aggregates. The data is then compared toreference curves to determine the degree of cataractogenesis.

In each of the above back scattering techniques, low intensity lightmust be incident upon the eye in order to avoid damage to the eye. Ofthe low intensity incident light, a portion thereof is reflected foranalysis. Because of the limited incident intensity, only a small amountof light is reflected back to a photomultiplier of limited quantumefficiency for measurement. The limited amount of reflected light andlimited quantum efficiency of the photomultiplier make accurate analysisdifficult.

Thus, a need exists for an improved, noninvasive, ocular disease statedetermination. The present invention meets this need by assessing thelight that reaches the patient's retina and forms the proximal stimulusthat the patient's visual system uses in the first stage of theperceptual process. The through-put quality of the axial portion of thelens is thereby measured indirectly by using the patient's visual systemas a visual null indicator that enables one to track the rate ofcataract formation. Use of the patient's retina itself as the detectorprovides a system of inherently superb quantum efficiency in contrast tothat of known photomultipliers.

Use of the patient's own retina as a detector, moreover, permits thedesign of an instrument and a method that employs light of higherenergy, of far shorter wavelength, e.g. 407 nm, during testing of thepatient's eye. This shorter wavelength light, which enters the patient'seye, enables assessment of optical properties and characteristics ofparticles of sizes far smaller than those able to be characterized bythe use of laser light of 633 nm wavelength.

DISCLOSURE OF THE INVENTION

Briefly, the present invention satisfies the above needs by providing amethod and apparatus enabling ocular disease state determination basedon light entering the patient's eye as the patient goes through a seriesof exercises to produce an exact color match between different lightmixtures in terms of hue, brightness and saturation.

In accordance with the above, it is an object of the present inventionto provide a noninvasive method for determining ocular disease states.

It is another object of the present invention to utilize the patient'sown perceptions of light in determining ocular disease states wherebythe patient acts as a null indicator.

It is yet another object of the present invention to provide a methodand an instrument to assess the precursor to cataract formation in theeye of a patient.

It is yet another object of the present invention to provide a methodand an instrument to enable the assessment of efficacy of any cataracttreatment and to estimate by how many years a non-surgical cataracttreatment (medical) has delayed cataract onset.

It is a further object of the present invention to provide a method andan instrument to detect risk factors which promote cataract formation.

It is still another object of the present invention to providequantitative analysis of a patient's judgement of light equality betweenadditive light mixtures to determine ocular disease states.

The present invention provides, in a first aspect, a method fordetermining a disease state in an eye of a patient. The method comprisesproviding a plurality of specific monochromatic lights for viewing bythe patient, observing the patient's color matching behavior for theplurality of lights and determining the extent of the disease statebased upon the patient's color matching behavior. The color matchesreflect the visual perceptions of the patient in accordance with thetransmissive characteristics of the patient's own eye, and inparticular, the lens of the patient's eye.

In a preferred embodiment of this first aspect of the present invention,each light of the plurality of the lights includes a mixture of twodifferent wavelength lights and at least one of the light mixtures isvaried as the patient's color matching behavior is observed. The step ofdetermining the disease state may comprise determining an existence ofthe disease, or it may comprise determining a severity or stage ofdevelopment thereof.

The present invention provides, in a second aspect, an apparatus forassisting in the determination of a disease state in an eye of apatient. The apparatus comprises a plurality of light sources andassociated filters, wherein each filter passes only a narrow range oflight of the associated light source about a particular wavelength. Aplurality of variable light attenuators are disposed in the optical pathof the respective filters for attenuating the associated filtered light.Additive mixers combine light as attenuated by given attenuators.Subsequent variable attenuators attenuate the combined light provided bythe additive mixers to provide resulting light mixtures of desiredbrightness. The resulting lights are directed to respective portions ofa photometer field adjacent to one another so that a patient may comparethe individual resulting light mixtures with respect to one another.Preferably, a chopper is provided in the light paths of the individuallight mixtures in alternating sequence such that the light mixtures arereceived at the photometer field sequentially one at a time. Acontroller of the apparatus enables the various light components of themixtures to be adjusted for effecting luminance levels of the associatedfiltered light components as provided, in the resulting light mixtures,to the photometer field. Finally, a radiometer is included for measuringthe power levels of the lights as presented to the patient within thephotometer field.

In a third aspect of the present invention, a method is provided fordetermining a disease state in an eye of a patient in accordance withthe patient's color matching behavior per different light polarizations.A first light mixture of first and second wavelength light components ismatched to a second light mixture of first and second light componentsas observed by the patient under test, wherein the first wavelengthlight component of the first light mixture is of a first polarizationstate. The polarization state of the first wavelength light component ofthe first light mixture is then changed and the light ratio of the firstlight mixture adjusted again until attaining a match between the firstand second light mixtures as perceived by the patient. The respectivelevels of the light components between the first match and the secondmatch are analyzed for determining the disease state of the eye.

These, and other objects, features and advantages of this invention willbecome apparent from the following detailed description of the variousaspects of the invention taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a light ray entering an eye and a backscattered rayexiting therefrom;

FIG. 2 is a two degree (2°) chromaticity diagram (after CIE) withparticular chords thereon;

FIG. 3A is a graph showing the effects of age on a primary measurementparameter for inferred lens photoluminescence of a given standardizationgroup;

FIG. 3B is a graph showing the accelerated effects relative tonon-diabetics of age on the primary measurement parameter for inferredlens photoluminescence for a second (albeit small) standardization groupof diabetics;

FIG. 4 is a graph similar to FIG. 3A showing the effects of age on asecondary measurement parameter for inferred lens photoluminescence ofthe given standardization group;

FIG. 5 is a partial flow chart illustrating a method in accordance withthe present invention for determining a disease state in an eye of apatient;

FIG. 6A is a continuation of the flow chart of FIG. 5 illustrating oneaspect for the method of the present invention;

FIG. 6B is a continuation of the flow chart of FIG. 5 illustrating analternative aspect for the method of the present invention;

FIG. 7 is a block diagram of an apparatus for assisting the method ofthe present invention;

FIG. 8 is a block diagram illustrating an apparatus for assisting analternative aspect for the method of the present invention; and

FIG. 9 is a block diagram illustrating a variable electro-opticpolarizer.

FIG. 10 depicts an apparatus for additive mixing of two lights 102A' and102C' in which the polarization angle produced by element 111 ismaintained to the extent of 96% at the eye of the patient 98.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIG. 1, a primarily spherical human eye 10 has macularegion of retina 26 at the internal rear surface of eye 10 and cornea 22provided at a forward circular region of eye 10. Crystalline lens 12 isdisposed just behind the cornea 22 with aqueous humor 24 therebetween.In the absence of a cataractous condition, the human in vivo crystallinelens 12 is relatively transparent. A cataract is defined asopacification of the crystalline lens that affects visual function. Thisopacification is thought to result from changes in the molecularstructure of the lens tissue. Except for those cataracts that resultfrom certain systemic or traumatic insult to the lens, the progressionof senile cataract (senile cataractogenesis) in humans is slow and mostof these cataracts become manifest as much as two decades before thedeath of a person (i.e. of an average life span expectancy).

Incident light ray 14 (of FIG. 1) enters cornea 22 at the front of eye10, passes through aqueous humor 24 and to crystalline lens 12. Iris 11provides an aperture that limits the area of lens 12 available forpassing received light. Backscattering particle 16 causes a portion 18of the incident light to return to and exit the front of eye 10. In thepast, cataract indicators have taken a generalized form of measurementdevice 20, which measures the amount of backscattered light 18 fordetermining the transparency (altered molecular structure) ofcrystalline lens 12. In a backscatter measurement, incident ray 14passes through cornea 22 and aqueous humor 24 before reaching a givendepth of the lens itself as associated with the backscattering. Afterdeflection, the backscattered light passes through the same path beforereaching indicator 20. Note that the backscattering measurements do notnecessarily reveal anything directly about the characteristics of thelight that reaches the macula retina 26 and hence can reveal littleregarding the degree of visual impairment produced by an incipientcataract.

Harding, J., "Cataract: Biochemistry, Epidemiology and Pharmacology", p.83 (Chapman and Hall, London, 1991) defines cataracts as lens opacitiesthat adversely affect visual function. Opacities that do not affectvisual function are classified solely as lens opacities. The latter areusually found in the peripheral or equatorial regions of older lenses.

In general, to maintain standard visual function, the intensity anddirection of a ray of light as it passes through the pupil and into, andthrough the lens must be preserved. To some extent backscattermeasurements will delineate changes in intensity of light that passesthrough the lens and also the changes in the direction of the light rayin passing through the lens. They will not, however, identify changes inthe wavelength of the light that enters the lens and excites the lens tophotoluminescence. Thus backscatter measurements fall short of acomplete delineation of the optical properties of the lens thatdetermine the retinal image in the immediate area of the visual axis,hence that determine visual function.

Moreover, because a cataract is a special species of opacity, byfocusing on the measurement of any opacity, backscattering studiesthemselves may give little information about the cataractogenic process.Only a method that is sensitive to the opacity precursor, and whichcharacterizes the light that directly reaches the macula thatimmediately surrounds the point of intersection with the visual axis 13of the eye, after passing through the part of the lens that is mostresponsible for the macula image, can provide information aboutcataractogenesis as defined by Harding. Thus, the backscatteringmeasurements are not an optimal indicator of the visual severity of acataract, possibly indicating a greater or lesser visual impairment thanthat actually suffered by a patient.

Visual acuity tests, which employ high contrast targets, also fall shortof completely characterizing visual dysfunctions suffered by a patientwith a cataract. For example, visual acuity under one set of lightingconditions may be minimally impaired by a cataract, yet totally impairedin the presence of a glare source, e.g., the headlights of an oncomingautomobile at night. As another example, a patient with a cataract maybe able to recognize a high contrast target, but be unable todistinguish low contrast features such as a face of another person a fewfeet away. Other visual dysfunctions experienced by patients withcataracts include bothersome dimness of vision, loss of colordiscrimination for the short wavelength end of the spectrum, and cloudedand indistinct vision. The onset of these dysfunctions may be so gradualthat their presence is recognized only after the cataractous lens isremoved and replaced with a lens that restores visual function. Thelatter visual dysfunctions are rarely detected by visual acuity teststhat use high contrast letters or figures, nor are they readilyidentified by backscatter measurements.

The present invention takes a different approach to cataractdetermination by assessing a throughput quality of a human crystallinelens as it affects color perception of a patient. Optical factorsaffecting the patient's color perception and color matching behaviorinclude absorption, scattering of light as it passes through the lens ofthe cataractous eye and photoluminescence from the lens as it impingesupon the retina. In the present invention, the throughputcharacteristics of a lens are inferred from a patient's color mixingbehavior in accordance with how much a given color mixture as providedby the patient differs from an age matched standard color mixture. Therationale for this inference rests upon the presumption that thethroughput characteristics of a lens are wavelength dependent, whichwavelength dependency affects the patient's perception of given colormixtures. In addition, it is presumed that the wavelength dependency ofa lens is affected by a cataract and its precursor conditions.Therefore, by determining the wavelength dependent characteristics ofthe lens, an assessment can be made of the presence, and/or stage ofdevelopment, of a cataract or its precursor conditions.

Before the specifics of the present invention are described, somebackground information regarding colorimetry as pertaining to thisinvention will be useful. Colorimetry is based upon many observations ofhuman additive color mixtures, the second described below, is especiallyrelevant to this invention. The first observation is that two separatelights of identical spectral make-up, whether of broad or narrow band,and of the same luminance, will, other things being equal, appearidentical to an observer. The second observation is that differentadditive mixtures, wherein each separate mixture consists of two or morespecifically selected lights of differing spectral composition, can beindividually adjusted in brightness such that the mixed lights appearindistinguishable, i.e., exactly matched to the same observer. To thoseskilled in the art, the lights of the first observation are known asnon-metameric, whereas the lights of the second observation are known asmetameric. These two observations taken together establish the corollarythat the perceived color of light is not solely governed by itswavelength composition, and that human color perception is non-analyticin the sense that it can not resolve a perceived color into itsidentifiable components (or Newton would not be remembered as the firstto show that sunlight can be decomposed into a multi-hued spectrum).

It is emphasized that the appearance of a given chromatic or achromaticlight is subjective. At present, no means for objective observation ofcolor perceptions is known. Nevertheless, additive mixtures of lightsthat give rise to metameric colors have been the focus of work by suchhistorical figures as Newton, Helmholtz, Maxwell, Grassman andSchroedinger. This work has been formalized in a graph known as the "CIEChromaticity Diagram," as reproduced in FIG. 2. See Judd and Wyszecki,Color and Business, Science and Technology, 3rd Ed., New York, 1975, andWright, The Measurement of Colour, 4th Ed., New York 1969.

With reference to FIG. 2, the area confined within the inverted`U`-shaped curve, 28, portrays all realizable colors obtainable bymixing single spectral wavelengths or very narrow bands of spectrallights. Curve 28 represents the coordinate positions of spectral lights,the so-called "spectrum locus" of colorimetry on the chromaticity graph.Those skilled in the art of colorimetry know that curve 28 is derivedfrom, summarizes, and is referable to the results of metameric colormatches made by observers with normal color vision, i.e., normaltrichromats. In making such mixtures these observers employed threeselected physical lights (e.g., a red, a green, and a blue light) tomatch all spectral and extra-spectral lights (the purples). It isGrassmann's Laws of Color Mixing that enable the creation of transformedimaginary primaries that form the bases of the CIE diagram. However, itis a long established axiom that a minimum of three additively mixablelights is required to match every spectral and extra-spectral (region36) color. Generally, these primaries are selected so that two (e.g., ared and a blue light) come from opposing ends of the spectrum and thethird (e.g. a green light) comes from the mid-region of the spectrum.The CIE Chromaticity Diagram illustrates for a given chromaticity, i.e.,hue and saturation, a relative level for two of the primaries along thex and y axes. When the graph represents an equal luminance plane, themagnitude of the third primary component (represented by a thirdperpendicularly related z axis not shown) can be derived from the levels(transformed) of the x and y imaginary primary components. The graph isnormalized wherein the algebraic sum of x, y and z is equal to 1.0.Thus, the various points within the curve may be specified withreference to two of the primaries (i.e., x and y) alone wherein thethird primary is derived according to the relationship of x+y+z=1. Notethat an equal energy white (for the "standard observer") on thechromaticity diagram has the coordinates of x=0.33, y=0.33 andaccordingly z=0.33. As used herein "real lights" or physical primaries,as contrasted to "imaginary lights" generally refer to lights mostproximate the spectrum locus or to mixtures represented as very near thespectrum locus. "Imaginary lights" or imaginary primaries refer tolights that are beyond the spectrum and the extra spectral loci.

Throughout much of the visible spectrum, i.e., from about 380 nm (point42 on curve 28) to about 540 nm (point 44 on curve 28), mixtures of twoof these primary spectral lights, one from the short wavelength region(a "blue") and one from the mid wavelength region (a "green"), willsubstantially match the color of a spectrum light lying on curve 28between points 42 and 44. The match will only be approximate, however,because its resulting mixture will appear desaturated relative to thespectrally purer light on the spectrum locus that the mixture isattempting to match.

The term desaturated refers to the appearance of a spectral light of afirst wavelength to which has been additively mixed one or more spectrallights of other wavelengths, well removed in the spectrum from the firstwavelength light. Such additions render the mixture desaturated. Aspectral light, represented as lying on curve 28, is by definition 100%saturated. Thus, to obtain an exact match of a light mixture of twospectrally removed lights (e.g., from the 380-540 nm region of curve 28)to a spectral light therebetween, it is necessary to desaturate thespectral light by the addition to it of at least a third light from the540-700 nm region of curve 28. Effectively this adds a "negative" amountof light to the mixture of the two spectrally removed lights within the380-540 nm region, making the intermediate spectral light less saturatedand bringing the two mixtures to an exact match within the area boundedby the spectral and extraspectral loci. (While it is most efficient touse the complementary wavelength to the intermediate spectral light forthis purpose, mixtures of other lights will serve as well, provided theydo not lie between the two from the 380-540 nm part of the spectrum.)

If a straight line 46 is drawn from point 43 on curve 28 (about 407 nm)to point 48 on curve 28 (about 500 nm), line 46 will represent the locusof all mixtures of spectral lights of 407 nm and 500 nm. If a lightmixture on line 46 is predominantly of 407 nm wavelength light, then wecan infer that the mixture will be perceived as similar to the blue orviolet region of the spectrum (by a color normal observer). On the otherhand, should the light mixture contain predominantly 500 nm wavelengthlight, it can be expected to appear greener to the same observer. Notethat line 46 drawn between the 407 nm point 43 of curve 28 and the 500nm point 48 of curve 28 does not pass through the equal energy spectrumregion, represented at coordinates x=0.33 and y=0.33; therefore,whatever the ratio of luminance of 407 nm light and 500 nm light, lightmixtures along line 46 can always be expected to appear chromatic, i.e.,to have an identifiable color when viewed by any color normal observer.

Line 50 is drawn from point 52 on curve 28 (about 480 nm) to point 54 oncurve 28 (about 580 nm), and represents all mixture ratios possible frommixtures of these two lights. If the mixture contains more light ofwavelength 480 nm relative to 580 nm wavelength light, it will appearbluer to a color normal observer, whereas it will appear yellower if itcontains more 580 nm light relative to the 480 nm light. At some ratioof the 480 nm light and the 580 nm light, the mixture can be representedby a point along line 50 proximate the coordinates (0.33, 0.33). It willthen appear achromatic. Any pair of spectral lights providing a lightmixture having such an achromatic quality is said to be a complementarypair.

There are three corollaries to the above additive color mixing rulespertinent to this invention. The first corollary is that any point noton curve 28, but within its confines, represents a light mixturecomprising two or more real spectral lights. The second corollary isthat any point within the confines of curve 28 can be represented by,and will be exactly matched in hue, saturation and brightness, by anumber of different combinations of real spectral lights, provided thatany such combination is adjusted to provide a mixture of the sameluminance as the mixture to which it is compared. For example, in FIG.2, point 58 can be represented by a mixture of, among others, 480 nm and580 nm wavelength light, or a mixture of 407 nm and 500 nm wavelengthlight. The third corollary is that if exactly matched, the sum of theluminances of the components of each of the two metameric mixtures areequal to each other. In other words, the total luminance of thecomponents of each of the composite lights of one pair will be equal tothat of the other pair.

It should be noted that the CIE system applies to normal trichromatswithout regard to their age, to their eye color, to their complexion(skin color), or to their gender. It also applies to all real lights ofthe visible spectrum and their mixtures.

A method according to one aspect of the present invention will now bedescribed with reference to testing an eye of a patient for a cataractor for the relative concentration of a cataract precursor. First, thepatient establishes monocularly, for the eye to be tested, an exactmatch between separate pairs of spectral lights in a two degree (2°)photometer field delivering all lights at a photopic level. Photopiclevel refers to a luminous level of a spectral light that is above thecolor threshold, and is generally considered to be of daylightintensity. For the purposes of the present invention, an exact match isone in which all parts of the photometer field appear identical in hue,saturation and brightness to the patient.

Although various spectral pairs of lights may be used for the patient toestablish a match, a first pair preferably comprises 407 nm (actually410 nm in one embodiment) wavelength light selected to maximally excitethe fluorophore of the human lens whose photoluminescent spectra peaksin the 490-530 nm range and a 500 nm wavelength light (hereinafter PairI). A second pair (hereinafter Pair II) comprises 480 nm wavelength(standard wavelength I) light and 580 nm wavelength (standard wavelengthII) light. As will be described more fully subsequently, theseparticular wavelength lights may be provided by white light that isfiltered by interference filters, or alternatively monochromators, withabout 10 to 15 nm Full Width Half Maximum (FWHM) bandwidths. Thefiltering provided by an interference filter can be tuned by pivotingthe filter slightly with respect to the longitudinal optical propagationaxis of light passing there through. This angular adjustment provides atranslation of the filter's associated peak spectral response from anormal wavelength to a new wavelength shifted by as much as severalnanometers. Although lights of such origins do not lie precisely on thespectrum locus, their departures therefrom do not significantly affectthe operation of this invention. An exact match between the first andsecond pairs is possible for a color normal observer since therespective chords of the two separate pairs intersect within theconfines of curve 28. It will be understood that, in practice, light ofexactly a given wavelength may not be possible with currently availableequipment; thus, some degree of wavelength flexibility is presumed. Suchflexibility in designated wavelengths will be deemed not tosignificantly impair the diagnostic capability of this instrument.However, the `violet` of Pair I should be about 407 nm, the `green` ofPair I should be about 500 nm, and the `blue` of pair II should be about480 nm with the `yellow` of Pair II, its complement, about 580 nm inthis embodiment.

Anyone asked to produce an exact color match with any type ofcolorimeter must be conversant with the vocabulary of color science ormade so by instruction. Some persons will readily understand therequirement that they are to adjust the instrument so that all parts ofthe photometer field appear uniform in color throughout. Others,however, will need more specific instruction for which the followingwill serve.

Seven approximately 2 inch discs, which have been coated with opaquepaints, comprise the instructional materials for a given user. Disc 1, 2and 3 are painted with a "sky" blue paint. Disc 4 is painted with aneven mixture of the above blue plus about 25% of a similar white paint.Disc 5 is painted with an even mixture of the above blue plus 3% of ablack paint. Disc 6 is painted with a green of approximately equalbrightness to the blue of disc 1, 2 and 3. Disc 7 consists of an evenmixture of 90% blue and 10% of the above green. Six of the 2 inch discs,namely, 2, 3, 4, 5, 6 and 7 are then bisected into hemi-discs.

Before beginning the instrumental test, the patient is presented withthe six pairs of hemi-discs, numbers 2-7, that have been randomlyarranged on a neutral gray surface (out of sight of the patient). Whenthese are brought into view, the patient is requested to look at thehemi-discs and to select the one, or ones, that match one of the halvesof disc number 2 so that the joined hemi-discs look like the uncut discnumber 1. If the patient selects the hemi-discs cut from number 3 or theother half of number 2, and only these, then it may be concluded thatthe request to establish an exact match in the colorimeter isunderstood. If not, then more replication, testing and instruction isrequired. It is further understood that if these same set of discs areto be reused, that they must not be soiled by handling. All discs mustbe replaced if wear and tear cause differential discoloration of disc 1and the hemi-discs of disc 2 and 3.

Once it is established that the patient understands what a color matchcomprises, the patient is provided in a first half of a two degree (2°)photometer field, a light mixture comprising the components of Pair I,and in a second half of the photometer field 480 nm wavelength lightalone (standard wavelength I). The patient is then requested to adjustthe power ratio of the components in the Pair I mixture so as to match,in hue, the 480 nm wavelength light.

Once this is done, 580 nm wavelength light (standard wavelength II),referred to as the desaturant, is added to the 480 nm light (providing aPair II mixture) until the patient perceives that the two halves of thephotometer field match closely in both hue and saturation. Once themixtures associated with the two halves of the photometer field havebeen matched closely, the patient is then permitted minimal adjustmentof all four lights in order to establish an exact match between themixtures of the respective photometer fields. In practice, it has beenobserved that most patients describe the color of these particularpairs, when matched, as resembling the clear northern sky. For a colornormal observer, the match of the two separate mixtures would berepresentative of point 58, in FIG. 2, where line 46 intersects line 50.

In greater particularity, the instrument presents four controls forpatient manipulation. For a patient not skilled in the art ofcolorimetry, a request to produce an exact match between the two partsof a photometer field could take a considerable length of time, even ifthe concept of an exact match is understood. Therefore, in order toassist the patient during the manipulative part of the task, the 480 nmwavelength light (standard wavelength I) component of Pair II is set tosome supra photoptic power level to serve as a reference, and the 407 nmwavelength light and 500 nm wavelength light of the Pair I light mixtureare then altered in a reciprocal fashion to one another so as tomaintain a constant luminance for the resulting mixture approximatelyequal to that of the 480 nm wavelength light reference (standardwavelength I). Neutral density wedges for attenuating the respectivelights are brought under the control of a microprocessor so that thepatient can set the 407-500 nm light mixture (Pair I) to match the hueof 480 nm wavelength light as closely as possible by a convergingstaircase or ramp procedure (up and down psychophysical method) via themicroprocessor.

The application of a microprocessor to control a converging (up anddown) staircase or ramp procedure is described by Ostrander et al; "APreferential Looking Clinical Acuity Test: Improvement in ImplementedMicrocomputer Control", Behavior Research Methods, Instruments, &Computers; 21 (4); 1989; pp. 421-425; hereby incorporated by reference.The microprocessor assisted procedure provides a differential responsebetween the two lights of the first mixture. If the mixture is too blueor violet, the patient responds by signaling the microprocessor toprovide more of the green primary light. The microprocessor then adjuststhe attenuation settings for the 407 nm wavelength light and the 500 nmwavelength light so that the 500 nm component is increased and the 407nm component decreased while preserving the total luminance of themixture. Conversely, if the mixture is too green, the patient signalsthe microprocessor to provide more blue.

Once a provisional match (in hue) to the 480 nm wavelength referencelight is achieved, the patient signals the microprocessor to add 580 nmwavelength light (standard wavelength II), the desaturant, to the 480 nmwavelength light (standard wavelength I). A new differential response isprovided by the microprocessor so that if the 480-580 nm light mixture,Pair II mixture, is too saturated, the patient signals themicroprocessor to provide more 580 nm wavelength light (standardwavelength II), and if the mixture is too desaturated, the patientsignals the microprocessor to supply less 580 nm wavelength light.Preferably, for each of the Pair I and Pair II mixtures, reciprocaladjustment of associated component neutral density attenuators isprovided by the microprocessor so that each resulting mixture has aconstant luminance as the mixture ratios are changed. The attenuatorsshould provide incremental adjustments of less than 4% and preferablyare continuously adjustable attenuators. After this provisionaladjustment for the Pair II mixture, the patient is then allowedindependent minimal adjustment of all four light components in order toobtain an exact match between the Pair I mixture and the Pair IImixture.

It should be noted that point 58, with reference to FIG. 2, at theintersection of lines 46 and 50, is not a color nor does it represent ageometric point. It merely represents the luminance ratios of the lightcomponents of the Pair I and Pair II mixtures that, to a color normalobserver, cause the two respective mixtures to appear indistinguishablein hue, saturation and brightness. In actuality, a finite area surroundsthe intersection of chords 46 and 50 within which a patient is unable todistinguish between the two separate mixtures.

After the patient has reported an exact match, between the Pair I andPair II mixtures, the light components of the Pair I mixture and 480 nmwavelength light (standard wavelength I) of the Pair II mixture arefixed at their corresponding levels that provided the match as set bythe patient. The luminance of the 580 nm wavelength light component(standard wavelength II) of the Pair II mixture is then adjusted to aluminance different from the previous match point. The patient is thenrequested to reestablish an exact match of the Pair II mixture to thePair I mixture by varying only the luminance of the 580 nm wavelengthlight component (standard wavelength II) relative to the fixed luminanceof the 480 nm wavelength light component. This sequence of offset andrematch is repeated a number of times, preferably 10 or so, in order tofurther establish that the patient understood the matching task and isable to provide a consistent match. The luminance of the 580 nmwavelength component (standard wavelength II) is determined and recordedfor each rematch. The mean and standard deviation for the luminancelevel of the 580 nm wavelength light from the above matching procedureare then computed. A standard deviation of more than about 4% of themean value indicates that either the matching task was not wellunderstood by the patient, or that the patient may have some form ofocular defect for which the present invention is not a suitablediagnostic method. When the standard deviation is outside the 4% range,the entire protocol is reperformed to rule out the possibility that thepatient has merely misunderstood the matching instructions. If thestandard deviation is within 4% of the mean value, then the procedurecontinues wherein the 580 nm wavelength light is adjusted to the meanluminance level. Note that in the preferred embodiment, the thresholdfor the standard deviation is set to 4% of the mean value; however, thepercentage used may change depending upon the instrument characteristicsbut should be well under 10% of the mean luminance value.

Assuming the standard deviation to be within the narrow range selected,the 407 nm wavelength light component of the Pair I mixture is replacedby a 440 nm wavelength light. The luminance levels of the other lights,the Pair II lights and the 500 nm wavelength light component of Pair I,remain fixed at the Pair I-Pair II matched levels. The mixture of the440 nm wavelength light and 500 nm wavelength light will hereinafter bereferred to as "Pair III". The luminance of the 440 nm wavelength lightis then adjusted so as to bring the two halves of the photometer field,the Pair II and Pair III mixtures, to a matching condition, as perceivedby the patient. Again, it is understood that point 58 in FIG. 2 is not,strictly speaking, an exact point, but rather a small area in colorspace within which an observer is unable to distinguish betweendifferent light mixtures. For practical purposes, any mixtures fallingwithin such an area are considered to be exactly matched. Once the PairIII mixture is matched to the Pair II mixture, the luminance level ofthe 440 nm wavelength light is determined. Note that any luminancedeterminations are based upon power level measurements of a radiometerin watts, divided by an associated area and then compensated by anassociated luminosity coefficient established in accordance with thewavelength of the light measured.

By assuming a normalized illuminated area of one for the area of thephotometer field illuminated by a given wavelength light component, theluminance value of each wavelength light component is determined bymultiplying the power level of the component by a luminosityco-efficient associated with the component's wavelength as shown herebelow in equation 1:

    L.sub.λ =V.sub.λ ×P.sub.λ       Eq. 1

L.sub.λ =Luminance at wavelength λ,

V.sub.λ =Luminosity coefficient at wavelength λ,

P.sub.λ =Power level of light at wavelength λ,

Luminosity coefficients are obtained from an available table referencingthe luminous efficiency of the eye with respect to the light'swavelength. See A.S.T.M. E-308, "Standard Practice for Computing theColors of Objects by Using the CIE System, Y.sub.λ =V.sub.λ exactly,Table-1, as provided here below.

    ______________________________________                                        λ                                                                           V.sub.M (λ)                                                                       λ                                                                              V.sub.M (λ)                                                                     λ                                                                           V.sub.M (λ)                      ______________________________________                                        380  0.20000E-03                                                                              415     0.11779E-01                                                                            450  0.46800E-01                             381  0.22821E-03                                                                              416     0.12842E-01                                                                            451  0.47743E-01                             382  0.26109E-03                                                                              417     0.13956E-01                                                                            452  0.48733E-01                             383  0.29936E-03                                                                              418     0.15111E-01                                                                            453  0.49785E-01                             384  0.34387E-03                                                                              419     0.16297E-01                                                                            454  0.50910E-01                             385  0.39556E-03                                                                              420     0.17500E-01                                                                            455  0.52122E-01                             386  0.45544E-03                                                                              421     0.18582E-01                                                                            456  0.53435E-01                             387  0.52462E-03                                                                              422     0.19645E-01                                                                            457  0.54864E-01                             388  0.60428E-03                                                                              423     0.20883E-01                                                                            458  0.56424E-01                             389  0.69565E-03                                                                              424     0.21694E-01                                                                            459  0.58131E-01                             390  0.80000E-03                                                                              425     0.22678E-01                                                                            460  0.60000E-01                             391  0.91635E-03                                                                              426     0.23636E-01                                                                            461  0.62601E-01                             392  0.10477E-02                                                                              427     0.24572E-01                                                                            462  0.65277E-01                             393  0.11955E-02                                                                              428     0.25490E-01                                                                            463  0.68042E-01                             394  0.13611E-02                                                                              429     0.26397E-01                                                                            464  0.709110-01                             395  0.15457E-02                                                                              430     0.27300E-01                                                                            465  0.73900E-01                             396  0.17508E-02                                                                              431     0.28335E-01                                                                            466  0.77016E-01                             397  0.18776E-02                                                                              432     0.29383E-01                                                                            467  0.80266E-01                             398  0.22273E-02                                                                              433     0.30442E-01                                                                            468  0.83666E-01                             399  0.25011E-02                                                                              434     0.31510E-01                                                                            469  0.87232E-01                             400  0.28000E-02                                                                              435     0.32584E-01                                                                            470  0.90980E-01                             401  0.31159E-02                                                                              436     0.33681E-01                                                                            471  0.94917E-01                             402  0.34576E-02                                                                              437     0.34735E-01                                                                            472  0.99045E-01                             403  0.38268E-02                                                                              438     0.35803E-01                                                                            473  0.10387E 00                             404  0.42256E-02                                                                              439     0.36860E-01                                                                            474  0.107884 00                             405  0.46562E-02                                                                              440     0.37900E-01                                                                            475  0.11260E 00                             406  0.51216E-02                                                                              441     0.38838E-01                                                                            476  0.11753E 00                             407  0.56248E-02                                                                              442     0.39675E-01                                                                            477  0.12267E 00                             408  0.61695E-02                                                                              443     0.40646E-01                                                                            478  0.12799E 00                             409  0.67597E-02                                                                              444     0.41524E-01                                                                            479  0.13345E 00                             410  0.74000E-02                                                                              445     0.42391E-01                                                                            480  0.13902E 00                             411  0.81451E-02                                                                              446     0.43252E-01                                                                            481  0.14467E 00                             412  0.89555E-02                                                                              447     0.44116E-01                                                                            482  0.15046E 00                             413  0.98322E-02                                                                              448     0.44990E-01                                                                            483  0.15646E 00                             414  0.10774E-01                                                                              449     0.45881E-01                                                                            484  0.16271E 00                             485  0.16930E 00                                                                              525     0.79320E 00                                                                            565  0.97860E 00                             486  0.17624E 00                                                                              526     0.80811E 00                                                                            566  0.97408E 00                             487  0.18355E 00                                                                              527     0.82249E 00                                                                            567  0.96917E 00                             488  0.19127E 00                                                                              528     0.83630E 00                                                                            568  0.96385E 00                             489  0.19941E 00                                                                              529     0.84949E 00                                                                            569  0.95813E 00                             490  0.20802E 00                                                                              530     0.86200E 00                                                                            570  0.95200E 00                             491  0.21719E 00                                                                              531     0.87381E 00                                                                            571  0.94545E 00                             492  0.22673E 00                                                                              532     0.88496E 00                                                                            572  0.93849E 00                             493  0.23685E 00                                                                              533     0.89549E 00                                                                            573  0.93116E 00                             494  0.24748E 00                                                                              534     0.90544E 00                                                                            574  0.92345E 00                             495  0.25860E 00                                                                              535     0.91485E 00                                                                            575  0.91540E 00                             496  0.27018E 00                                                                              536     0.92373E 00                                                                            576  0.90700E 00                             497  0.28229E 00                                                                              537     0.93209E 00                                                                            577  0.89827E 00                             498  0.29505E 00                                                                              538     0.93992E 00                                                                            578  0.88920E 00                             499  0.30857E 00                                                                              539     0.94722E 00                                                                            579  0.87978E 00                             500  0.32300E 00                                                                              540     0.95400E 00                                                                            580  0.87000E 00                             501  0.33840E 00                                                                              541     0.96025E 00                                                                            581  0.85986E 00                             502  0.35468E 00                                                                              542     0.96600E 00                                                                            582  0.84939E 00                             503  0.37169E 00                                                                              543     0.97126E 00                                                                            583  0.83862E 00                             504  0.38928E 00                                                                              544     0.97602E 00                                                                            584  0.82758E 00                             505  0.40730E 00                                                                              545     0.98030E 00                                                                            585  0.81630E 00                             506  0.42552E 00                                                                              546     0.98409E 00                                                                            586  0.80479E 00                             507  0.44430E 00                                                                              547     0.98748E 00                                                                            587  0.79308E 00                             508  0.46339E 00                                                                              548     0.99031E 00                                                                            588  0.78119E 00                             509  0.48293E 00                                                                              549     0.99281E 00                                                                            589  0.76915E 00                             510  0.50300E 00                                                                              550     0.99495E 00                                                                            590  0.75700E 00                             511  0.52356E 00                                                                              551     0.99671E 00                                                                            591  0.74475E 00                             512  0.54451E 00                                                                              552     0.99809E 00                                                                            592  0.73242E 00                             513  0.56569E 00                                                                              553     0.99911E 00                                                                            593  0.72000E 00                             514  0.58696E 00                                                                              554     0.99974E 00                                                                            594  0.70749E 00                             515  0.60820E 00                                                                              555     0.10000E 00                                                                            595  0.69490E 00                             516  0.62934E 00                                                                              556     0.99885E 00                                                                            596  0.68221E 00                             517  0.65030E 00                                                                              557     0.99930E 00                                                                            597  0.66947E 00                             518  0.67087E 00                                                                              558     0.99832E 00                                                                            598  0.65674E 00                             519  0.69084E 00                                                                              559     0.99689E 00                                                                            599  0.64384E 00                             520  0.71000E 00                                                                              560     0.99500E 00                                                                            600  0.63100E 00                             521  0.72818E 00                                                                              561     0.99260E 00                                                                            601  0.61815E 00                             522  0.74546E 00                                                                              562     0.98974E 00                                                                            602  0.60531E 00                             523  0.76196E 00                                                                              563     0.98644E 00                                                                            603  0.59247E 00                             524  0.77783E 00                                                                              564     0.98272E 00                                                                            604  0.57963E 00                             605  0.56680E 00                                                                              534     0.13920E 00                                                                            685  0.11920E-01                             606  0.55396E 00                                                                              646     0.13150E 00                                                                            686  0.11068E-01                             607  0.54113E 00                                                                              647     0.12502E 00                                                                            687  0.10273E-01                             608  0.52835E 00                                                                              648     0.11877E 00                                                                            688  0.95333E-02                             609  0.51563E 00                                                                              649     0.11276E 00                                                                            689  0.88461E-02                             610  0.50300E 00                                                                              650     0.10700E 00                                                                            690  0.82100E-02                             611  0.49046E 00                                                                              651     0.10147E 00                                                                            691  0.76237E-02                             612  0.47803E 00                                                                              652     0.96218E-01                                                                            692  0.70854E-02                             613  0.46567E 00                                                                              653     0.91122E-01                                                                            693  0.65914E-02                             614  0.45340E 00                                                                              654     0.86264E-01                                                                            694  0.61384E-02                             615  0.44120E 00                                                                              655     0.81600E-01                                                                            695  0.57230E-02                             616  0.42908E 00                                                                              656     0.77120E-01                                                                            696  0.53430E-02                             617  0.41703E 00                                                                              657     0.72825E-01                                                                            697  0.49957E-02                             618  0.40503E 00                                                                              658     0.68710E-01                                                                            698  0.46764E-02                             619  0.39303E 00                                                                              659     0.64769E-01                                                                            699  0.43800E-02                             620  0.38100E 00                                                                              660     0.61000E-01                                                                            700  0.41020E-02                             621  0.36891E 00                                                                              661     0.57396E-01                                                                            701  0.38384E-02                             622  0.35682E 00                                                                              662     0.53955E-01                                                                            702  0.35890E-02                             623  0.34477E 00                                                                              663     0.50673E-01                                                                            703  0.33542E-02                             624  0.33281E 00                                                                              664     0.47549E-01                                                                            704  0.31340E-02                             625  0.32000E 00                                                                              665     0.44580E-01                                                                            705  0.29290E-02                             626  0.30933E 00                                                                              666     0.41758E-01                                                                            706  0.27381E-02                             627  0.29785E 00                                                                              667     0.39084E-01                                                                            707  0.25598E-02                             628  0.28659E 00                                                                              668     0.36583E-01                                                                            708  0.23924E-02                             629  0.27562E 00                                                                              669     0.34200E-01                                                                            709  0.22372E-02                             630  0.26500E 00                                                                              670     0.32000E-01                                                                            710  0.20910E-02                             631  0.25476E 00                                                                              671     0.29962E-01                                                                            711  0.19535E-02                             632  0.24488E 00                                                                              672     0.28076E-01                                                                            712  0.18245E-02                             633  0.23533E 00                                                                              673     0.26329E-01                                                                            713  0.17035E-02                             634  0.22605E 00                                                                              674     0.24708E-01                                                                            714  0.15901E-02                             635  0.21700E 00                                                                              675     0.23200E-01                                                                            715  0.14840E-02                             636  0.20816E 00                                                                              676     0.21800E-01                                                                            716  0.13844E-02                             637  0.19954E 00                                                                              677     0.20501E-01                                                                            717  0.12912E-02                             638  0.19115E 00                                                                              678     0.19281E-01                                                                            718  0.12040E-02                             639  0.18297E 00                                                                              679     0.18129E-01                                                                            719  0.11227E-02                             640  0.17500E 00                                                                              680     0.17000E-02                                                                            720  0.10470E-02                             641  0.16722E 00                                                                              681     0.15903E-01                                                                            721  0.97658E-03                             642  0.15964E 00                                                                              682     0.14837E-01                                                                            722  0.91110E-03                             643  0.15227E 00                                                                              683     0.13810E-01                                                                            723  0.85013E-03                             644  0.14512E 00                                                                              684     0.12834E-01                                                                            724  0.79323E-03                             ______________________________________                                    

For the Pair I and Pair III lights, the following proportions arecalculated: ##EQU1## where L₅₀₀ is the compensated luminance for theincident 500 nm wavelength light component of the Pair I and Pair IIImixtures respectively; L₄₀₇ is the compensated luminance for theincident 407 nm wavelength light component of the Pair I mixture; andL₄₄₀ is the compensated luminance for the incident 440 nm wavelengthlight component of the Pair III mixture.

It will be apparent to one skilled in the art of colorimetry that thechords drawn in FIG. 2 from the 407 nm point and the 440 nm point oncurve 28, each to the 500 nm point, are essentially equal in length.They differ by only 1% and, therefore, the Pair I and Pair III luminanceproportion ratios would be expected to be essentially the same for anylens. However, in actuality, these ratios differ from one another inaccordance with the stage of cataractogenesis.

FIGS. 3A and 4 are graphs plotting, with respect to age, Pair I and PairIII luminance proportions respectively for the results of color matchesmade by 16 European Caucasian American men as a standardization group.They had no visual complaints and wore no corrections when they made thecolor matches. Preferably separate curves are obtained forstandardization groups of particular eye colors and/or complexions forcomparison with subjects of similar eye color and/or complexion. The twoasterisks 63 and 65 of FIG. 3A represent data points of a 72 year oldsubject with a PMMA plastic intraocular lens and a 64 year old subjectwith a surgically mature cataract respectively, which data points areused for comparative purposes only and are not taken as part of thestandardization group. It should be noted that the proportions plottedin FIG. 3A were obtained using 410 nm wavelength light in the Pair Imixture instead of a preferred wavelength of 407 nm. The Pair Iproportions are plotted in FIG. 3A, and the Pair III proportions areplotted in FIG. 4. Both are plotted with respect to the age of thesubject.

Curve 66 is a curve of best fit for the Pair I proportions, and curve 64is the 95% prediction interval therefor. Standard curve fittingtechniques may be employed for fitting a curve to the data points of thestandardization group. For example, in one embodiment, curve 66 wasobtained per a generalized equation 4 as follows:

    K.sub.o +K.sub.1 exp(K.sub.2 *Age)                         Eq. 4

Similarly, curve 62 is a curve of best fit for the Pair III proportions(FIG. 4). The best fit lines 62 and 66 show that each ratio decreaseswith increasing subject age. It is believed that the departure from anequality prediction for both is due to absorption of the shorterwavelength light by the lens and a proportion thereof being converted byphotoluminescence.

Artisans skilled in the arts of measurement theory, scaling theory andpsychometric methods will know the techniques for developing astandardization curve for values of a standardization group. Afterobtaining standardization curves for mixture ratio values of astandardization group, wherein associated luminosity data has beencompensated by the above luminosity coefficients, corresponding mixtureratio values taken from a patient under test are compared against thestandardization curve and the extent of the differences therebetween areused to determine whether or not a cataract or cataract precursorcondition exists within the given patient. These differences are relatedto the differences between points 63 and 65 in FIGS. 3A and 4. Inaddition, the proportion values obtained for patients of different agesunder test are used to determine the rate of cataractogenesis. Theproportions determined are matched to the age equivalent values of thestandardization group curves. The slope of the standardization groupcurve at the value corresponding to that determined for the patient istaken as the stage of cataractogenesis for the patient. Again, it shouldbe noted that the standardization function shown is for a group ofEuropean-Caucasian American men. Different standardization functions maybe expected from groups of different eye colors or complexions.Different functions may, moreover, be obtained for the women and men ofthose groups.

Examples of proportion comparisons are shown with reference to FIG. 3A,wherein a Pair I proportion obtained from a 64 year old man with asurgically mature cataract with significant visual acuity impairment,and a Pair I proportion for a 72 year old patient with an intra-ocularPMMA lens, both European-Caucasian men, are plotted with reference tothe standardized plots of the standardization group comprising the 16European-Caucasian American men. The marks of both men, in FIG. 3A, fallbeyond their respective 95% prediction interval limits of thestandardized data. The Pair I ratio asterisk 63, for the patient withthe inter-ocular lens is above the standardized curves 66 and 64 whilethe Pair I ratio, asterisk 65, for the cataract patient falls below thestandardized curves 66 and 64. Thus, the curve for the standardizedgroup (which falls between the marks of the respective sample patients)depicts a rate of development for the concentration of a cataractprecursor from the immature concentration level at an early age to theformation of a senile cataract at a later age.

By comparing the ratio values of a test patient to an appropriatestandardization curve, the stage of cataract development, the rate ofcataractogenesis and cataract onset prediction can be determined inaccordance with the placement of the test patient's values relative tothe standardization curve. A patient's Pair I ratio value relative theratio value span between points 63 and 65, i.e. the 72 year old man withthe inter-ocular lens and the 64 year old man with cataract respectivelyin FIG. 3A, indicates the state of cataractogenesis. The slope of thestandardization curve at a ratio value corresponding to the ratio valueof the test patient provides a rate of cataractogenesis. The number ofyears along the standardized curve from a first point of a ratio valuethereof corresponding to the test patient's ratio value to a secondpoint of a ratio value corresponding to a mature cataract provides atime prediction for an onset of cataracts for the test patient. Finally,the number of years offset between the test patient's ratio value to apoint of equivalent value on the standardization curve provides thenumber of years of accelerated/retarded cataractogenesis.

FIG. 3B shows a standardization curve drawn for a second standardizationgroup of diabetics. A curve was fit to the Pair I ratio values obtainedfrom three diabetic patients. Note that there appears to be anaccelerated rate of cataractogenesis in comparison with the associatedcurves of the standardization group of FIG. 3A.

Thus far, polarization effects have been ignored. However, the fullutility of the present invention can be realized, in accordance with asecond aspect of the present invention, by considering how color mixtureratios are affected in accordance with polarization of one member of thePair I mixture. Varying the polarization of light entering the eye froma vertical polarization to a horizontal polarization is believed tocause a change in the forward small particle scattering intensity.Therefore, color matches made with light of different polarizationslikewise yield differences in corresponding mixture ratios. This followsfrom the fact that, in a relative sense, forward scattering is markedlyincreased in a lens where substantial phase separation has occurred.Such conditions exist in an advanced stage of a maturing cataract. Thisagrees with observed results wherein older subjects produced greaterratio differences between polarization states than that of youngerpatients. It has been observed that the polarization affects uponmixture ratios is wavelength dependent. In other words, changing thepolarization state of 407 nm wavelength light (excitation light forphotoluminescence) changes the Pair I mixture ratio value while changingthe polarization state of the 440 nm wavelength light has littleinfluence upon the Pair III ratio value. Accordingly, the method andinstrument in accordance with one aspect of the present invention willtake into account the polarization of the 407 nm wavelength lightcomponent as the patient performs respective color matches.

With reference to FIG. 7, an apparatus in accordance with the presentinvention enables a patient to mix light sources for matching lightmixtures of given color ratios from which the presence of a cataract orcataract precursor is determined as described hereinbefore. Variouslight sources 102 are supplied to filters 104 which filter the lightsources to supply desired wavelength light components as necessary forforming mixtures to be incident to photometer field 114. The variouswavelength light components as produced are not polarized. Primaryattenuators 106 attenuate various filtered light components before thevarious light components are mixed by mixers 108A and 108B. The lightmixtures from mixers 108A and 108B are attenuated by secondaryattenuators 110A and 110B before being incident upon respective portions118, 120 of photometer field 114. Preferably, chopper 109 is interposedin the light paths between mixers 108A,108B and respective portions118,120 of photometer field 114. The chopper blocks respective lightpaths in alternating sequence so that photometer field 114 receives theassociated light of mixers 108A,108B in alternating sequence. Thechopping rate for the chopper is set to be well above the flicker fusionrate. A patient views the respective light mixtures as incident uponphotometer field 114 with his/her eye 98 that is being tested.Radiometer 112 measures the power of light as incident upon photometerfield 114.

Controller 100, such as a microprocessor, controls various elements ofthe system in order to supply respective light mixtures upon photometerfield 114. The line drawn from controller 100 to attenuator 106E isassumed to represent a plurality of control lines to respectiveattenuators 106A-106E. Likewise, the line from controller 100 toattenuator 110B represents control lines to both attenuator 110A andattenuator 110B. Assuming a light mixture of 407 nm wavelength light and500 nm wavelength light are desired to be incident upon a first portion118 of photometer field 114, then controller 100 will enable lightsources 102A and 102C. Light sources 102A and 102C provide incidentwhite light upon respective filters 104A and 104C. Filter 104A filtersthe white light of light source 102A preferably to output 407 nmwavelength light. Filter 104C on the other hand receives white lightfrom light source 102C and outputs therefrom a spectral light componentcentered at 500 nm wavelength preferably ±5 nm. Respective attenuators106A and 106C attenuate the individual filtered light components inaccordance with desired ratios selected by operator 122 via controller100. In one aspect of the present embodiment, the attenuator settingsare adjusted differentially such that the total luminance output (theattenuated components combined) is equal to a constant. For example,assume that the combined luminance for the 407 nm wavelength light andthe 500 nm wavelength light is to be equal to one, and that theoriginating luminance incident upon respective attenuators is likewiseequal to one. If attenuator 106A provides an attenuation level of 0.7,attenuator 106C should therefore provides an attenuation level of 0.3 sothat the resulting luminance output for the combined components is equalto 1.0.

The outputs from attenuator 106A and attenuator 106C are broughttogether by mixer 108A whereupon the resulting mixture is thenattenuated by attenuator 110A which is controlled by controller 100. Sowhile attenuators 106A and 106C provide the ratio of spectral componentsto be summed by mixer 108A, attenuator 110A on the other hand attenuatesthe combined light mixture until a desired combined power is measured bymeter 112 (note that meter 112 may be separate from the instrument).

In producing this first light mixture, the 407 nm wavelength light and500 nm wavelength light are summed together while no component isprovided by the 440 nm wavelength light. Accordingly, controller 100disables light source 102B as incident upon filter 104B, oralternatively provides full level attenuation by attenuator 106B so thatthere is no 440 nm wavelength light supplied to mixer 108A. Furthermore,if it is necessary to measure the power of the first light mixture assupplied to the first portion 118 of photometer field 114, thencontroller 100 can disable light sources 102D and 102E, or alternativelyprovide full attenuation to attenuator 110B while meter 112 takes apower measurement of the light projected onto photometer field 114.

When it is necessary to provide a light mixture of 440 nm wavelengthlight and 500 nm wavelength light, light sources 102B and 102C areenabled for providing white light incident upon filters 104B and 104C.Filter 104B filters the white light of light source 102B to provide 440nm wavelength light, preferably at a λ-max of 440 nm+5/-1 nm. Filter104C filters the white light of light source 102C to output 500 nmwavelength light as described hereinbefore.

Controller 100 provides a ratio for the 440 nm wavelength light withrespect to the 500 nm wavelength light via the attenuation settings ofattenuators 106B and 106C. The 407 nm wavelength light component isturned off by either disabling light source 102A or providing fullattenuation by attenuator 106A. Mixer 108A mixes the attenuated 440 nmwavelength light from attenuator 106B and the attenuated 500 nmwavelength light provided from attenuator 106C whereupon the resultingmixture is attenuated by attenuator 110A. Again, attenuator 110A iscontrolled by controller 100 to assure a desired output power asmeasured by meter 112. The above two illustrated examples characterizethe optical channels required for generating the Pair I and Pair IIIlight mixtures respectively irrespective of polarization.

To generate the Pair II light mixture, the lower optical mixing chain isoperated in a manner similar to the upper optical mixing chain. Lightsources 102D and 102E provide white light incident upon filters 104D and104E respectively. Filter 104D filters the white light of light source102D to provide an output wavelength light centered at 480 nm preferably±1 nm at peak. Filter 104E filters the white light of light source 102Eto provide an output wavelength light centered at 580 nm preferably ±1nm at center. The 480 nm wavelength light is incident upon attenuator106D while the 580 nm wavelength light is incident upon attenuator 106E.Controller 100 adjusts the attenuation ratios between attenuators 106Dand 106E, preferably in a differential manner with respect to oneanother, such that the total output luminance of the two componentscombined is equal to a constant. The attenuated 480 nm wavelength lightcomponent and the 580 nm wavelength light component are combined bymixer 108B to produce a resulting output light mixture incident uponattenuator 110B. Controller 100 sets the attenuation level of attenuator110B so that the light incident upon a second portion 120 of photometerfield 114 has a predetermined power. Note that to measure the powerlevels of the Pair II light mixture components, the Pair I and Pair IIIlight mixtures are disabled so that meter 112 measures only Pair IIImixture light components as incident upon the second portion 120 ofphotometer field 114. The controller can turn off the Pair I and PairIII light mixtures by disabling light sources 102A, 102B, and 102C oralternatively by providing full attenuation by attenuators 106A, 106B,and 106C and/or providing full attenuation by attenuator 110A. Thus,photometer field 114 only receives light of the Pair II light mixturewhich is measured by radiometer 112.

In taking power measurements of the light components of a given lightmixture, only one light wavelength component is enabled at a time whilemeter 112 obtains a power measurement (watts). To obtain the associatedluminance value for the light component, the measured power is dividedby the illuminated area of the photometer field and multiplied by aluminosity coefficient as associated with the wavelength of the lightcomponent as described hereinbefore, supra page 27. The luminositycoefficient is related to the human luminous efficiency characteristicswith respect to wavelength of the light.

In an alternative aspect of the present invention, with reference toFIG. 8, a variable electro-optic polarizer 111 is disposed in theoptical path of the 407 nm wavelength light (the shorter wavelengthlight) for controlling the polarization of the 407 nm wavelength lightas presented onto photometer field 114. Preferably, electro-opticpolarizer 111 is positioned in the optical path of the 407 nm wavelengthlight after filter 104A and before attenuator 106A. However, one skilledin the art will understand that electro-optic polarizer 111 could bepositioned just before filter 104A or after attenuator 106A so long asit affects the polarization of only the 407 nm wavelength light.

Electro-optic polarizer 111 preferably comprises, with reference to FIG.9, a neutral density polarizer 113 followed by a variable pi-cell 115.Neutral density polarizer passes light of one polarization, e.g.horizontal H, to analyzer 115. Analyzer 115 receives the polarized lightfrom polarizer 113 and provides essentially no effect on thepolarization of the light, or changes the polarization of the polarizedlight from the horizontal to vertical, so long as the light is within agiven bandwidth as associated with the analyzer. Polarized light may bethought of as comprising two components of opposite circularly polarizedlight, i.e. left circular polarization e^(jwt) and right circularpolarization e^(-jwt). The analyzer comprises an electro-opticcrystalline material that has different velocities for right circularlypolarized light and left circularly polarized light propagating along agiven axis thereof, when the crystalline material is under the influenceof an applied electric field. Absent an applied electric field, thevelocities for the two separate circularly polarized lights are assumedequal. Assuming light of a given frequency, an electro-optic crystallinematerial (i.e. analyzer) of a given thickness, and an associated appliedelectric field across the analyzer; a retardation of π radians (180°)can be provided for one of the circularly polarized lights relative theother. Under such circumstances linearly polarized light passingtherethrough will have its polarization altered by 90°. Such a variableelectro-optic polarizer is available from Oriel Corporation.Alternatively, electro-optic polarizer could be a mechanically rotatedpolarizer.

Variable optical polarizer 111 receives 407 nm wavelength light fromfilter 104A and polarizes the light exiting therefrom in accordance witha control voltage received from controller 100. Preferably, variableoptical polarizer passes linearly polarized light of either horizontalor vertical polarization in accordance with the control voltage receivedfrom controller 100.

As described hereinbefore, respective attenuator pairs of either theupper optical mixing path or the lower optical mixing path aredifferentially operated to provide constant luminance outputs for theresulting mixture. However, once a close match is established betweenrespective light mixtures, the operator is allowed limited individualcontrol of the separate attenuators (via the controller 100) so that thepatient observing the photometer field 114 is able to adjust theattenuators for obtaining an exact match between the respective colormixtures as incident upon the first and second regions 118,120respectively of photometer field 114.

In a preferred embodiment of the present invention, light sources 102are Tungsten Halogen light(s) for providing white light to respectivefilters 104. It will be apparent to one skilled in the art, thatindividual light sources 102A, 102B, 102C, 102D, 102E could be replacedby a single white light source with individual light paths to thevarious filters so long as the intensity of white light provided to therespective filters 104 is stable. Such light sources are available fromGeneral Electric, Nela Park, Cleveland, Ohio.

Filters 104 are quarter wavelength dielectric layered interferencefilters that receive white light and pass a spectral light componentthereof in accordance with the thickness of the quarter wavelengthdielectric layers of the interference filters, and have a peak pass bandresponse that can be shifted slightly by changing the angle ofinclination of the filter's surface with respect to the incident light.Such interference filters are readily available from Corion Corp.Alternatively, the filters are monochromators which break white lightinto narrow bands of particular wavelength components. Suchmonochromators are available from Spex Industries, Inc. It will beunderstood to one skilled in the art, that light sources 102 andrespective filters 104 could be replaced with other means for producingspectrally pure light, such as a laser source with appropriate diffusion(coherence breaking) and polarization means.

The attenuators are standard variable attenuators such as neutraldensity wedges as are available from Oriel Corp., Stratford, Conn.Again, the respective attenuators should have incremental adjustments ofless than 4% neutral density and preferably are continuously adjustableattenuators.

A skilled artisan will know that additive mixing of colored lights maybe accomplished by several means. Any of these means will satisfy themixing requirements for the light channel associated with attenuator110B (FIG. 8). The same artisan will know that some of these mixingmethods that may be satisfactory for use in the 110B channel, e.g., anintegrating sphere or a similar optical device, will not be satisfactoryfor mixing light for the channel associated with attenuator 110A. Suchmixers, as the integrating sphere, do not maintain the polarization oflight inducted by polarizer 111 once it has entered and exited.

In a preferred embodiment of the present invention, mixer 108A preservesthe polarization angle of light reaching the patient's eye by 96% ormore, as measured by the power of the light reaching a radiometerlocated where the patient's eye 98 would be (i.e., beyond 114). Such amixer arrangement 108A is shown in FIG. 10, where the mixing isaccomplished by a beam splitter 150 that redirects the light of twocoaxial congruent projection light sources 102A',102C' to a common focusat a given distance onto a (finely ground) glass screen, photometerfield 118. One half of the bipartite photometer field 114 receives theredirected light 152 from mixer 108A. The beam splitter 150 consists ofa glass plate that is strain-free and inclined at 45° to the lightprojection axis of projector 102A. In this arrangement more than 96% ofthe light from projector 102A sustains the polarization angle producedby polarizer 111 after passing through screen 118 on its way to thepatient's eye.

In the preferred embodiment of the present invention, before photometer114 and after the two mixers 108A,108B, a beam chopper 109 (FIG. 8) isinterposed which presents the different light mixtures of mixers108A,108B onto respective portions photometer fields 118 and 120 withlight inputs that are chopped 180° out of phase with respect to eachother. The integration qualities of the eye of an observer are such thatthe chopping condition of the light is not noticeable so long as thelight is chopped at a rate above the flicker fusion rate. By providingalternative light mixture projections onto respective portions 118,120of photometer field 114, the instantaneous perception of one colormixture of one field will not be influenced by photoluminescence in thelens as might be caused by a primary light of the mixture as projectedonto the other field.

With reference to FIGS. 5 and 6a, a first method of the presentinvention is provided for determining a cataract or a cataract precursorcondition of a patient. In step 70, the test apparatus is calibrated forlight of a standard wavelength I. To initiate step 70, an operatorsignals controller 100 (of FIG. 7) to provide 480 nm light, standardwavelength I, onto second portion 120 of photometer field 114.Controller 100 responds by turning on light source 102D and adjustingattenuators 106D and 110B for providing a given luminance of the 480 nmwavelength light on the second portion of photometer field 114. Duringthis calibration adjustment, all other attenuators are set to their fullattenuation settings and/or the light sources 102A-102C and 102E aredisabled. Next, an integer M is set to an initial state of 0, step 72.

With the light of standard wavelength I properly adjusted, a lightmixture, i.e. Pair I, is projected onto the first portion 118 ofphotometer field 114. The Pair I light mixture comprises an additivelymixed combination of 407 nm wavelength light and 500 nm wavelength lightas provided via respective optical paths. The patient views photometerfield 114 as controller 100 adjusts (per operator inputs) theattenuation levels of the respective light components until the Pair Ilight mixture, as incident upon the first portion 118 of the photometerfield 114, has a hue corresponding to the hue of the 480 nm light, asprojected onto the second portion 120 of photometer field 114, asobserved by the patient. Once the hue of the Pair I light mixturematches most closely the hue of the 480 nm light, the patient under testsignals the controller to record and set the various attenuator settingsof the optical path associated with the Pair I light mixture, i.e.attenuators 104A, 104C and 110A, thus establishing the Pair I mixture(step 71).

It is assumed that the apparatus has been precalibrated so thatcontroller 100 can determine the power level of a given light componentreaching photometer field 114 in accordance with its associatedattenuator (and polarization) settings. During such precalibration,controller 100 enables one wavelength light component at a time,disabling all other wavelength lights, and calibrates the variousattenuator (and polarization) settings in accordance with the powerreceived at photometer field 114 as measured by radiometer 112.Alternatively, controller 100 may repeat respective component powermeasurements directly as needed instead of indirectly deriving suchpower levels from the attenuator (and polarization) settings andassociated precalibration tables.

Next, in step 74, 580 nm wavelength light, standard wavelength II, iscombined with the 480 nm wavelength light, standard wavelength I, so asto desaturate the color of the 480 nm spectral light and provide a PairII light mixture of color more closely matching that of the previouslyestablished set Pair I light mixture. During this operation, controller100 adjusts (step 77) the attenuator settings of attenuators 106D and106E in preferably a differential manner until the saturation level ofthe Pair II light mixture (as projected onto the second portion 120 ofphotometer field 114) corresponds to the saturation provided by the PairI light mixture (as projected onto the first portion 118 of photometerfield 114). Attenuator 110B is adjusted to obtain the desired totalluminance of the Pair II light mixture. When controller 100 provides therequired ratio for matching (step 76) most closely the saturation of thePair II light mixture with the Pair I light mixture, as observed by thepatient under test, the patient then signals controller 100 to stopfurther adjustment. In one embodiment of the present invention, thepatient is then permitted limited control of attenuators 106A, 106C,106D, and 106E until obtaining an "exact" color match. The patient (orclinician conducting the test) then signals the controller to record allof the attenuator settings associated with providing the Pair II lightmixture, i.e. step 78. Integer M is then incremented by one in step 80.

In step 82, integer M is examined to determine whether or not it isequal to 10. After a first iteration, M is equal to 1 and system controlmoves to step 84 wherein the luminance of the 580 nm wavelength lightcomponent, standard wavelength II, of the Pair II light mixture ischanged randomly, while leaving the luminances of the other three lightsfixed. Control moves back to step 74 wherein adjustment of the 580 nmwavelength light is made until obtaining the desired saturation again.The intensity settings of the 580 nm light should be made randomly aboveand below the last adjustment point, i.e. for providing Pair II lightmixtures that are too desaturated and too saturated relative the Pair Imixture. These steps of adjusting the level of the 580 nm wavelengthlight and re-matching the light mixture of Pair II to the mixture ofPair I are repeated a plurality of times with the respective attenuatorsettings being recorded after each iteration until integer M is equal to10. An artisan will understand that the number of iterations to beperformed could be a number other than 10 so long as the number ofiterations is suitable for statistical purposes to obtain a useful meanand standard deviation thereof. After the tenth iteration, the mean andstandard deviation for the power level of the 580 nm wavelength light,standard wavelength II, required for affecting the desired saturationlevel are computed in step 86 and examined in step 88 to determinewhether or not the standard deviation is within an acceptable range. Ifthe standard deviation is not within an acceptable range, it isdetermined either that the patient has a visual system defect thatprecludes diagnosis with this method or did not understand the matchingprocedure, whereupon control transitions back to beginning step 70 sothat the process may be initialized and performed all over again to ruleout the possibility that the patient has merely misunderstood thematching principles. Alternatively, the testing procedure could beterminated and a message directed to the operator that such terminationcondition has been reached. It is anticipated that this instrument andmethod will be effective even for patients with protan and deutan colorvision defects and be inapplicable to persons with achromatopsia ortritan defects.

Assuming that the standard deviation calculated in step 86 is within anacceptable pass range, process flow transitions to step 90 (FIG. 6a)wherein the level of the 580 nm wavelength light is set to its meanvalue as calculated in step 86 and the 480 nm and 500 nm lights are setto the levels associated with the above match. In step 91, the 440 nmwavelength light replaces the 407 nm wavelength light component of thePair I light mixture for providing a new Pair III light mixture to beincident upon the first portion 118 of photometer field 114. In step 92,the level of the 440 nm wavelength light is then adjusted via attenuator106B in order to effect a desired mixture in the first portion 118 ofphotometer field 114 exactly matching the Pair II light mixture asincident upon the second portion 120 of photometer field 114. Thisadjustment procedure is continued between decision step 94 and operatingstep 92 until a match is obtained between the respective light mixturesas observed by the patient. Once the match has been obtained, processflow moves to step 96 wherein the luminance levels of the spectralcomponents making up the Pair III light mixture are determined andrecorded. In accordance with one aspect of this embodiment of thepresent invention, the luminance levels are obtained from direct powermeasurements, obtained by meter 112 with individual light componentsbeing directed alone upon photometer field 114. Alternatively, theapparatus is precalibrated wherein controller 100 can determine theluminance levels of individual light components based upon therespective attenuator (and polarization) settings alone.

In step 136 proportions are computed between the light components of thePair III light mixture and the Pair I light mixture as describedhereinbefore. The ratio for the Pair I light mixtures is computedaccording to the luminance of its 500 nm wavelength light component overthe sum of the luminance of the 407 nm and the 500 nm wavelength lights.The ratio computed for the Pair III mixture is equal to the luminance ofits 500 nm wavelength light component divided by the sum of theluminance of the 500 nm wavelength light component and the 440 nmwavelength light. The luminance value of each wavelength light componentis determined by multiplying the power level of the component by aluminosity coefficient associated with the components wavelength asdescribed hereinbefore, supra page 27.

Groups of observers (subjects) who have no cataracts and who belong to asingle demographic group, e.g. Oriental women with dark eyes, African(American) men with very dark eyes etc., are used to develop separatestandardization groups. As in FIG. 3, their ages need to cover a broadrange of ages, especially the 60-85+ that constitute the ages of thosemost likely to be tested for senile cataract. Similarly, patients fromeach of these groups who have surgically extracted or surgically maturecataracts are employed to provide validation data for each demographicgroup.

In step 138, the computed ratios for the patient under test are comparedto corresponding ratios of subjects without identified cataracts of anage matching the patient under test. It is then determined whether ornot the computed ratios are within a given prediction interval of theratios for those without cataracts, per step 140. If the computed ratiosare below the prediction interval of this group, then an interpretationis made regarding the cataract condition of the patient (step 142) andreported to the clinician conducting the test. If the ratios are withinthe prediction level of this group, then controller 100 reports anabsence of cataracts for the patient and terminates the test procedure.

In a first alternative aspect of this embodiment of the presentinvention, the computed ratios for the patient are compared tostandardized data of a standardization group to provide informationregarding the stage of cataractogenesis. The proximity of the patient'scomputed ratios relative to the predetermined ratios of a juvenilesubject, or a subject with an intra-ocular lens, and a mature subjectwith cataracts indicates the stage of cataractogenesis for the patientbetween the juvenile stage and the mature stage.

In accordance with a second alternative aspect of this embodiment of thepresent invention, a rate of cataractogenesis is determined. Employing apredetermined standardized curve that maps ratio values with respect toage for a standardized group, the slope of the standardized curve at aratio value corresponding to the patient's determined ratio value istaken as representative of the rate of cataractogenesis.

In accordance with a third alternative aspect of this embodiment of thepresent invention, a determination is made regarding the number of yearsby which the patient's cataractogenesis is accelerated or retarded withrespect to a predetermined standardized curve of a standardizationgroup. A time offset in number of years is determined between thepatient's determined ratio value and a corresponding point on thestandardized curve. This time offset is taken as the number of years bywhich the patient's cataractogenesis has been accelerated or retarded,depending upon which side of the curve the patient's ratio valueresides.

In accordance with a fourth alternative aspect of this embodiment of thepresent invention, an estimation is provided of the number of yearswithin which the patient may develop cataracts. An equivalent point islocated on a predetermined standardized curve of a standardization groupin accordance with the patient's ratio value. The number of years alongthe standardized curve from the equivalent point to a value thereofassociated with cataracts is taken as an estimation of the number ofyears within which the patient may develop cataracts.

With reference to FIGS. 5, 6B and 8, a second method of the presentinvention is provided for determining a cataract or a cataract precursorcondition of a patient. Steps 70 through 90 are performed in the samemanner as described hereinbefore except that the 407 nm wavelength lightcomponent of the Pair I mixture is linearly polarized by variableelectro-optic polarizer 111 (FIG. 8) in either H or V mode. Controller100 sets the control voltage to variable electro-optic polarizer 111,which is in the optical path of the 407 nm wavelength light, so as tolinearly polarize the 407 nm light in a first polarization state, i.e.,either vertically or horizontally.

Assuming the patient is able to consistently provide color matchesbetween the Pair I light mixture and the Pair II light mixture, suchthat the standard deviation calculated in step 86 is within anacceptable range as examined in step 88, then control transitions tostep 90, with reference to FIG. 6B, wherein the level of the 580 nmwavelength light is set to its mean value as calculated in step 86.Next, in step 144, the polarization state of the 407 nm wavelength lightcomponent of the Pair I light mixture is changed, e.g., from horizontalto vertical or vice versa. Controller 100 changes the control voltageapplied to variable electro-optic polarizer 111 so that it imparts asecond polarization state to the 407 nm wavelength light.

The levels of the new Pair I light mixture, having the 407 nm wavelengthlight component of the second polarization state, are adjusted per step92' via attenuators 106A and 106C until the new light mixture (in thefirst portion 118 of photometer field 114) matches, per step 94, thePair II light mixture (as incident upon the second portion 120 ofphotometer field 114) as observed by the patient under test. Once thecolor match has been obtained, control transitions to step 96 whereinthe luminance levels of the new polarized 407 nm wavelength light andthe 500 nm wavelength light components of the new Pair I light mixtureare determined and recorded. Again, the levels of the various lightcomponents can be determined by direct measurements using meter 112, orindirectly in accordance with respective attenuator (and polarization)settings and respective predetermined calibration tables as describedhereinbefore.

In step 136' respective ratios are computed between the light componentsof the original Pair I light mixture (having the 407 nm wavelength lightof the first polarization state) and the new Pair I light mixture(having the 407 nm wavelength light of the second polarization state).The ratio for the original Pair I light mixture is computed according tothe luminance of its 500 nm wavelength light component divided by thesum of the luminance of the 407 nm wavelength light component of thefirst polarization state and the 500 nm wavelength light. The ratiocomputed for the new Pair I mixture is equal to the luminance of its 500nm wavelength light component divided by the sum of the luminance of the407 nm wavelength light component of the second polarization state andthe 500 nm wavelength light. Again, the luminance levels are preferablycomputed according to the product of determined power levels andassociated luminosity coefficients as described hereinbefore, supra page27.

In step 138', the computed ratios are compared to corresponding ratiosof a standardization group of age matching the patient under test. Suchstandardizations and validations are required for the differentpolarization angles as well. It is then determined in step 140 whetheror not the computed mixture proportions are within a given predictioninterval of the proportions for the standardized group, and anappropriate cataract interpretation (step 142) is reported to theclinician conducting the test similarly as described before.

In both methods of the embodiments described hereinbefore, again it ispreferable that the light mixtures as incident upon respectivephotometer fields 118 and 120 be incident in alternating sequence sothat light of one mixture will not affect the patient's perception ofthe other mixture. As described in a previous embodiment, suchalternating sequencing of light mixture can be provided by chopper 109.

It will be understood that some patients will require corrective lenses.Accordingly, the apparatus and methods of the present invention shouldprovide standard trial lenses for correcting subject vision withmaterials that do not significantly differentially absorb norphotoluminesce under the influence of the spectral lights employedwithin the present invention.

It will be understood that many changes to the elements of system 96 arepossible by one skilled in the art. For example, attenuators 106 and/or110 may be neutral density filters under patient, operator and/ormicroprocessor control. Also, in some instances, light mixtures of PairI and Pair III could be matched directly in one step, eliminating thepreliminary match between the mixtures of Pair I and Pair II.

The Pair I and Pair III ratios obtained using the 407+500 nm and the440+500 nm mixtures respectively, both vary with patient and lensthereof. However, the Pair I and Part III ratios are differentiallyaffected by the cataractogenic process. Perturbations in the 407+500 nmPair I mixture with age are more pathognomonic of the two, andaccordingly are used for diagnosis and assessment of a disease asdescribed hereinbefore. This differential effect is presumed to be dueto the fact that this mixture of wavelengths is selected to capitalizeon a well-identified lens fluorophore. However, perturbations due tocataractogenesis also occur, but to a lesser degree, in the 440+500 nmPair III ratios. Accordingly, further test methods determine theperturbation differentials between the Pair I and Pair III ratios, andemploy them for differential diagnoses. Suitable standardizations andvalidation data for these differential diagnosis must be available foruse in this manner.

While several aspects of the present invention have been described anddepicted herein, alternative aspects may be effected by those skilled inthe art to accomplish the same objectives. Accordingly, it is intendedby the appended claims to cover all such alternative aspects as fallwithin the true spirit and scope of the invention.

We claim:
 1. A method for determining a disease state in an eye of apatient, comprising the steps of:providing a plurality of metamericlights for viewing by said patient, each light comprising a lightmixture of at least two different wavelength components, each componenthaving an associated luminance value; determining a proportion ofassociated luminance values of components of a select light of saidplurality of lights when said select light is adjusted to match anotherof said plurality of lights as reported by said patient; and determiningsaid disease state based on said proportion by referencing saidproportion to predetermined data of a standardization group,representative of standard proportions with respect to age of thestandardization group, and determining an acceleration or retardation ofsaid disease state in accordance with relative placement of saiddetermined proportion to corresponding standard proportions of saidpredetermined data.
 2. A method according to claim 1 wherein saidpatient reports said match as observed with said eye.
 3. A methodaccording to claim 2, wherein said disease state is a cataract andwherein said step of determining said disease state comprisesdetermining a stage of cataract formation based on said proportion ofsaid select light.
 4. A method according to claim 1 wherein acorrelation to diabetes is provided by referencing said proportion tothe predetermined data.
 5. A method according to claim 1 furthercomprising varying a light mixture of said select light to achieve saidmatch.
 6. A method according to claim 1 wherein one light of saidplurality of lights excites a fluorophore of a lens associated with theeye of said patient.
 7. A method according to claim 1 wherein said stepof providing a plurality of lights includes providing at least one lightof said plurality of lights with a given polarization.
 8. A methodaccording to claim 1 wherein at least one light component of saiddifferent wavelength light components of said select light mixture isprovided a given polarization.
 9. A method according to claim 8 furthercomprising:varying said given polarization of said at least one lightcomponent, and then adjusting said select light to achieve a secondmatch.
 10. A method according to claim 9 wherein matches are provided bysaid patient with said given polarization at different polarizationstates and at corresponding levels of said polarized light component asrequired to match the light mixture of the select light with anotherlight mixture of said plurality of lights.
 11. A method according toclaim 10 wherein said matches comprise color matches.
 12. A methodaccording to claim 1 wherein said step of providing a plurality oflights includes supplying for view by said patient at least two lightsin alternating sequence in respective fields of view of said patient.13. A method according to claim 1 wherein said step of determining saiddisease state comprises determining an existence of said disease state.14. A method according to claim 1 wherein said step of determining saiddisease state comprises determining an extent of said disease state. 15.A method according to claim 1 wherein said step of determining saiddisease state comprises determining a development rate of said diseasestate.
 16. The method of claim 1, wherein a luminance value of acomponent is determined by dividing a power level measurement by anassociated photometric field area and then multiplying by a luminositycoefficient related to the luminous efficiency of the eye with respectto the wavelength of the component.
 17. The method of claim 16, whereinsaid proportion comprises a ratio of a luminance value of one componentof said select light to a sum of the luminance values of components ofsaid select light.
 18. A method for determining a disease state in aneye of a patient, comprising steps of:providing a first light and asecond light for viewing by said patient, each of said first light andsaid second light comprising a mixture of at least two lights, each ofsaid at least two lights having a different wavelength; varying saidmixture of said second light to a first set ratio where said patientreports that said first light and said second light appearindistinguishable; replacing said second light with a third lightcomprising a mixture of at least two lights, each of said at least twolights having a different wavelength; adjusting said mixture of saidthird light to a second set ratio where said patient reports that saidfirst light and said third light appear indistinguishable; anddetermining said disease state based on said first set ratio and saidsecond set ratio.
 19. A method according to claim 18, wherein said stepof providing provides said first light and said second lights inalternating sequence in respective first and second fields of view ofsaid patient.
 20. A method according to claim 18, wherein said step ofvarying comprises altering the luminance levels differentially betweeneach of said at least two lights until obtaining said first set ratio ofsaid second light;wherein said step of adjusting comprises altering theluminance levels differentially between each of said at least two lightsuntil obtaining said second set ratio of said third light; and whereinsaid step of determining comprises:determining first luminance levelsfor respective wavelength light components of said second light andsecond luminance levels for respective wavelength light components ofsaid third light; and determining first and second set ratios based onsaid first luminance levels and said second luminance levelsrespectively.
 21. A method according to claim 19 wherein said step ofdetermining the first luminance levels includes determining a primarypower level for one of said lights making up the mixture of said secondlight and multiplying this primary power level by an associatedluminosity coefficient to provide a primary luminance level, anddetermining a secondary power level for another one of said lightsmaking up the mixture of said second light and multiplying thissecondary power level by an associated luminosity coefficient to providea secondary luminance level;said step of determining the secondluminance levels includes determining a primary power level for one ofsaid lights making up the mixture of said third light and multiplyingthis primary power level by an associated luminosity coefficient toprovide a primary luminance level, and determining a secondary powerlevel for another one of said lights making up the mixture of said thirdlight and multiplying this secondary power level by an associatedluminosity coefficient to provide a secondary luminance level; said stepof determining said first set ratio comprises dividing, for the mixtureof said second light, said primary luminance level by the sum of saidprimary luminance level and said secondary luminance level; and saidstep of determining said second set ratio comprises dividing, for themixture of said third light, said primary luminance level by the sum ofsaid primary luminance level and said secondary luminance level.
 22. Amethod according to claim 21, wherein said step of determining saiddisease state comprises interpreting a cataract condition based upon acomparison of said first set ratio and said second set ratio relative tocorresponding ratios of a standardization group.
 23. A method accordingto claim 22 wherein said comparison is made relative to thestandardization group at an age corresponding to an age of said patient.24. A method according to claim 18 wherein said step of determiningfurther comprises a step of interpreting a cataract condition based onsaid first and second set ratios.
 25. A method according to claim 18wherein said step of determining said disease state accounts for an ageof said patient.
 26. A method according to claim 18 wherein said step ofdetermining comprises interpreting a cataractogenic rate based on saidfirst and second set ratios relative respectively to characteristiccurves of a standardization group.
 27. A method for determining adisease state in an eye of a patient, comprising steps of:providing afirst light mixture of first and second wavelength light components;providing a second light mixture of two different wavelength lightcomponents; setting a polarization of at least said first wavelengthlight component of the first light mixture to a first polarization;adjusting to first set levels the levels of said first and secondwavelength light components wherein said first light mixturesubstantially matches said second light mixture as reported by saidpatient; changing the polarization of said first wavelength lightcomponent of the first light mixture to a second polarization; adjustingto second set levels the levels of said first and second wavelengthlight components where said first light mixture again substantiallymatches said second light mixture as reported by said patient; anddetermining said disease state based on said first set levels and saidsecond set levels.
 28. A method according to claim 27 wherein said stepof changing the polarization provides substantially a 90° change inpolarization status.
 29. A method according to claim 27 wherein saidfirst polarization is vertical/horizontal polarization and said secondpolarization is horizontal/vertical polarization, respectively.
 30. Amethod according to claim 27 wherein said step of determining saiddisease state includes:determining mixture ratios on the basis of saidfirst set levels and said second set levels; comparing said mixtureratios to predetermined corresponding ratios of a standardization group;and interpreting said disease state on the basis of said comparison. 31.A method according to claim 30 wherein said step of interpreting saiddisease said does so on the relative placement of said mixture ratiosrelative corresponding ratios of a first reference patient having anintra-ocular PMMA lens and a second reference patient having asurgically ripe cataractous lens.
 32. An apparatus for assisting anevaluation of a disease state in an eye of a patient, comprising:meansfor providing a plurality of metameric lights, each metameric lightcomprising a mixture of at least two different wavelength lightcomponents; adjustment means for varying a light mixture of a principallight of said plurality of metameric lights to match a light mixture ofa secondary light of said plurality of metameric lights as observedthrough said eye and determined by said patient; means for determining aratio of luminance levels of components of said matching light mixtureof said principal light; and means for determining the presence of saiddisease state by comparing said ratio to predetermined datarepresentative of reference light mixtures required of a standardizationgroup to match said principal light to said secondary light.
 33. Anapparatus according to claim 32 wherein said match is based on hue,saturation and brightness, and said ratio comprises a luminance level ofone component of said matching light mixture of said principal lightdivided by a sum of luminance levels of components of said matchinglight mixture of said principal light.
 34. An apparatus according toclaim 32 wherein said means for providing further comprises choppermeans for providing said principal light and said secondary light inalternating sequence in respective first and second fields of view ofsaid patient.
 35. An apparatus according to claim 33, further comprisingmeans for determining a luminance level of a component by dividing apower level measurement by an associated photometer field area and thenmultiplying by a luminosity coefficient related to the luminousefficiency of the eye with respect to the wavelength of the component.36. An apparatus according to claim 32 wherein said means fordetermining the presence of said disease state includes reference meansfor storing and recalling predetermined reference light mixture data forthe standardization group with respect to age, said means fordetermining the presence of said disease state compares said determinedratio of luminance levels of the matching light mixture to thepredetermined data of the reference light mixture of the reference meansfor the standardization group of an age corresponding to an age of saidpatient.
 37. An apparatus according to claim 32 wherein said means forproviding a plurality of lights includes:means for providing whitelight; means for filtering the white light, yielding primary spectralcomponents thereof; and means for combining select primary spectralcomponents to provide said principal light and said secondary light. 38.An apparatus according to claim 37 further comprising polarization meansfor effecting a polarization of light in the optical path of at leastone of said primary spectral components.
 39. An apparatus according toclaim 37 wherein the means for filtering comprises a plurality ofinterference filters of various wavelength selectivities disposed inrespective optical paths of said white light.
 40. An apparatus accordingto claim 37 wherein the means for filtering comprises a monochromatorfor splitting said white light into respective spectral componentsthereof.
 41. An apparatus according to claim 37 wherein said means forfiltering yields a first primary spectral component of wavelengthassociated with an excitation spectrum of a flourophore of the eye ofsaid patient.
 42. An apparatus according to claim 41 wherein said meansfor filtering further provides a second primary spectral component ofwavelength associated with a flourophore emission spectrum of the eye ofsaid patient.
 43. An apparatus according to claim 42 wherein said meansfor combining combines said first primary spectral component with saidsecond primary spectral component to provide said principal light. 44.An apparatus according to claim 37 wherein said means for filteringprovides a primary spectral component of wavelength associated with aflourophore emission spectrum of the eye of said patient.
 45. Anapparatus according to claim 32 wherein said adjustment means includesmeans for adjusting the luminance of two spectral components of saidlight mixture differentially while maintaining a given total luminancefor said principal light.
 46. An apparatus for assisting an evaluationof a disease state in an eye of a patient, comprising:a first lightsource providing a first light of a first wavelength band; a secondlight source providing a second light of a second wavelength banddiffering from the first wavelength band; a third light source providinga control light of a given hue and a given saturation; first and secondattenuator means for variably attenuating the respective first andsecond light of said first and said second light sources and providingattenuated first light and attenuated second light accordingly; mixermeans, coupled to receive the attenuated first light from said firstattenuator means and the attenuated second light from said secondattenuator means, for optically combining the attenuated first light andthe attenuated second light and providing a combination thereof as aprincipal additively mixed light; control means for adjusting said firstand said second attenuators until said principal additively mixed lightsubstantially matches said control light in hue, saturation andbrightness as observed through said eye and determined by said patient;and means for determining respective luminance values of said attenuatedfirst light and attenuated second light when said principal additivelymixed light substantially matches said control light, said luminancevalues being determined with luminosity coefficients reflecting theluminous efficiency of an eye with respect to light wavelength.
 47. Anapparatus according to claim 46 further comprising means for determininga mixture ratio of said luminance values of said first and said secondlight making up said principal additively mixed light when saidprincipal additively mixed light is matched to said control light asreported by said patient.
 48. An apparatus according to claim 47 furthercomprising means for comparing said determined mixture ratio tocorresponding predetermined mixture ratio data of a standardized groupof an age similar to an age of said patient and providing informationregarding a state of said disease in accordance with said comparison.49. An apparatus according to claim 46 wherein said first wavelength ofsaid first light strongly stimulates a fluorophore having a strong 407nm absorption and an emission peak at about 500 nm in the lens of theeye of said patient.
 50. An apparatus according to claim 46 wherein saidfirst wavelength strongly stimulates a fluorophore in a lens of the eyeof said patient and said second wavelength is of an associatedphotoluminescent spectrum of said lens.
 51. An apparatus according toclaim 50 wherein said first wavelength is about 407 nm, said secondwavelength is greater than 490 nm, and said control light is of a hueclose to a 480 nm wavelength light.
 52. An apparatus according to claim46 further comprising polarizer means for affecting a polarization ofsaid first light component of said principal additively mixed light. 53.An apparatus according to claim 46 further comprising:a photometer fieldhaving a first region for receiving said principal additively mixedlight for view by said patient and a second region for receiving saidcontrol light for view by said patient; and chopper means forsequentially chopping said principal additively mixed light and saidcontrol light in alternating sequence so to be provided for view in therespective first and second regions of the photometer field inalternating sequence.
 54. An apparatus according to claim 53 furthercomprising meter means for measuring power of light incident upon saidphotometer field.
 55. Apparatus for assisting determination of a diseasestate in an eye of a patient, comprising:a plurality of light sources; aplurality of filters, each filter allowing only light of about aparticular wavelength from said plurality of light sources to passtherethrough; a plurality of variable attenuators for attenuatingassociated filtered light from said plurality of filters; a pair ofadditive mixers for combining light from said plurality of attenuators;a photometer field for receiving associated combined light fromrespective mixers for view by said patient; a controller for controllingsaid plurality of light sources, and said plurality of variableattenuators to establish hue, saturation and brightness for saidcombined lights as received by said photometer field for comparison andmatching by said patient; and means for varying one of wavelength andpolarization of light received by at least one of said additive mixers.56. An apparatus according to claim 55 wherein said plurality of filterscomprise quarter wavelength interference filters.
 57. An apparatusaccording to claim 55 wherein said plurality of filters comprises amonochromator.
 58. An apparatus according to claim 55 further comprisinga radiometer for measuring power of light components received by saidphotometer field.
 59. An apparatus according to claim 55, wherein saidmeans for varying comprises a polarization means for effectingpolarization of a given filtered light as received at said photometerfield.
 60. An apparatus according to claim 59 wherein said polarizationmeans effects polarization of said filtered light of shortestwavelength.
 61. An apparatus according to claim 59 wherein saidpolarization means is adjustable between two separate polarizationstates comprising vertical and horizontal.
 62. An apparatus according toclaim 61 wherein the polarization state of said polarization means iscontrolled by said controller.
 63. An apparatus according to claim 59wherein one filter of said plurality of filters passes light of awavelength that most strongly excites the fluorophore of a lens of theeye of said patient and said polarizer means is in the same optical pathas said one filter for effecting a polarization of said light that moststrongly excites that fluorophore.
 64. An apparatus according to claim63 wherein said one filter passes light of a wavelength of about 407 nm.65. An apparatus according to claim 55 further comprising chopper meansfor chopping said associated combined light from respective mixers inalternating sequence so that said associated combined light from therespective mixers as chopped by said chopper means are received by saidphotometer field for view by said patient in alternating sequence. 66.An apparatus according to claim 55 further comprising secondary variableattenuators between said additive mixers and said photometer field forcontrolling the intensity of said combined lights from the respectivemixers that is received by said photometer field.
 67. A method fordetermining a stage of cataract formation in an eye of a patientcomprising the steps of:providing a plurality of metameric lights forviewing by said patient, each light comprising a light mixture of atleast two different wavelength components, each component having anassociated luminance value; determining a proportion of associatedluminance values of components of a select light of said plurality oflights when said select light is adjusted to match another of saidplurality of lights as reported by said patient; and determining a stageof cataract formation based on said proportion.
 68. A method fordetermining a disease state in an eye of a patient, comprising the stepsof:providing a plurality of metameric lights for viewing by saidpatient, each light comprising a light mixture of at least two differentwavelength components, each component having an associated luminancevalue; providing a component of a select light of said plurality oflights with a given polarization; determining a proportion of associatedluminance values of components of the select light when said selectlight is adjusted to match another of said plurality of lights asreported by said patient; and determining said disease state based onsaid proportion.